Could Human Evolution Have Been Affected by Glacial Maximum?

[Count Iblis]

We all know about some of the important roles vitamin D plays in the body. The question is why the body uses vitamin D (or rather calcitriol which the body produces from Vitamin D) to act as a switch to turn on the production of certain proteins that are involved in the absorption of calcium from our food? If these proteins are so important, why is the production of these proteins made dependent on vitamin D?

 

[DaveC426913]

Because we evolved on a planet with a sun? If we'd evolved underground, we'd have a different mechanism.

IU'm not really sure why you're asking 'why?'.

 

[Count Iblis]

You don't get any vitamin D at all at higher lattitudes during the winter months and part of spring and fall. In Canada everyone is adviced to take vitamin D supplements (people with a dark skin during the whole year). This is because there is now a lot of evidence that the higher level of vitamins D that people have at lower lattitudes play a role in preventing some diseases (to keep your bones healthy you don't need such high vitamin D levels).

Vitamin D only activates certain genes. The question is then why the body has evolved to use vitamin D which you can so easily get a shortage of.

 

[DaveC426913]

You don't get any vitamin D at all at higher lattitudes during the winter months and part of spring and fall. In Canada everyone is adviced to take vitamin D supplements (people with a dark skin during the whole year). This is because there is now a lot of evidence that the higher level of vitamins D that people have at lower lattitudes play a role in preventing some diseases (to keep your bones healthy you don't need such high vitamin D levels).

Vitamin D only activates certain genes. The question is then why the body has evolved to use vitamin D which you can so easily get a shortage of.

Do you mean in modern society, or in human history? It's a bigger problem now that we spend more time indoors.

The body has a number of dependencies, Vitamin C for example. What is special about this one?

 

[Proton Soup]

it seems vitamin D has been with us for a long time, but we're not entirely sure why.

i think it's also fairly new knowledge that vitamin D receptors are ubiquitous throughout the body.

Recent Results Cancer Res. 2003;164:3-28.
Evolution and function of vitamin D.

Holick MF.

Vitamin D Laboratory, Section of Endocrinology, Diabetes and Nutrition, Department of Medicine, Boston University Medical Center, Boston, MA 02118, USA. mfholick@bu.edu

It is remarkable that phytoplankton and zooplankton have been producing vitamin D for more than 500 million years. The role of vitamin D in lower non-vertebrate life forms is not well understood. However, it is critically important that most vertebrates obtain an adequate source of vitamin D, either from exposure to sunlight or from their diet, in order to develop and maintain a healthy mineralized skeleton. Vitamin D deficiency is an unrecognized epidemic in most adults who are not exposed to adequate sunlight. This can precipitate and exacerbate osteoporosis and cause the painful bone disease osteomalacia. Once vitamin D is absorbed from the diet or made in the skin by the action of sunlight, it is metabolized in the liver to 25-hydroxyvitamin D [25(OH)D] and then in the kidney to 1,25-dihydroxyvitamin D [1,25(OH)2D]. 1,25(OH)2D interacts with its nuclear receptor (VDR) in the intestine and bone in order to maintain calcium homeostasis. The VDR is also present in a wide variety of other tissues. 1,25(OH)2D interacts with these receptors to have a multitude of important physiological effects. In addition, it is now recognized that many tissues, including colon, breast and prostate, have the enzymatic machinery to produce 1,25(OH)2D. The insights into the new biological functions of 1,25(OH)2D in regulating cell growth, modulating the immune system and modulating the renin-angiotensin system provides an explanation for why diminished sun exposure at higher latitudes is associated with increased risk of dying of many common cancers, developing type 1 diabetes and multiple sclerosis, and having a higher incidence of hypertension. Another calciotropic hormone that is also produced in the skin, parathyroid hormone-related peptide, is also a potent inhibitor of squamous cell proliferation. The use of agonists and antagonists for PTHrP has important clinical applications for the prevention and treatment of skin diseases and disorders of hair growth.

PMID: 12899511 [PubMed - indexed for MEDLINE]

 

[Count Iblis]

Do you mean in modern society, or in human history? It's a bigger problem now that we spend more time indoors.

The body has a number of dependencies, Vitamin C for example. What is special about this one?

I think vitamin C is directly participating in anti-oxidation processes. But as I understand it, vitamin D does nothing more than to act as a signal telling cells to produce certain proteins that are involved in regulating calcium absorption from food, regulate the immune system etc. as the article quoted by Proton-Soup mentions.

 

[f95toli]

So?

Remember that humans have lived in a warm a and sunny climate for most of our history, so getting enough vitamin D was not a problem. This means there was no evolutionary pressure to "develop" an alternative mechanism.

 

[DaveC426913]

So?

Remember that humans have lived in a warm a and sunny climate for most of our history, so getting enough vitamin D was not a problem. This means there was no evolutionary pressure to "develop" an alternative mechanism.

More eloquently put than mine.

 

[Count Iblis]

http://en.wikipedia.org/wiki/Vitamin_D#Biochemistry"

Production of vitamin D in nature always appears to require the presence of some UV light; even vitamin D in foodstuffs is ultimately derived from organisms, from mushrooms to animals, which are not able to synthesize it except through the action of sunlight at some point in the synthetic chain. For example, fish contain vitamin D only because they ultimately exist on calories from ocean algae which synthesize vitamin D in shallow waters from the action of solar UV.

It is not clear to me why evolution would have led to all higher organisms making very critical processes dependend on vitamin D given that one can easily get shortages and given that the vitamin D derived calcitriol only acts as a mere switch. It is like a company hiring very highly skilled personell to do trivial work that could be done by everyone or be completely automated.

The only explanation I can think of is that there is evolutionary pressure against using easy to produce compounds to regulate the processes that vitamin D regulates. If the receptors to which calcitriol binds were replaced by different receptors so that other molecules would bind to it and those other molecules would be manufactured without sunlight by certain cells in the organism itself, then perhaps this process would be very vulnerable to diseases in which the molecules are overproduced.

 

[Proton Soup]

http://en.wikipedia.org/wiki/Vitamin_D#Biochemistry"



It is not clear to me why evolution would have led to all higher organisms making very critical processes dependend on vitamin D given that one can easily get shortages and given that the vitamin D derived calcitriol only acts as a mere switch. It is like a company hiring very highly skilled personell to do trivial work that could be done by everyone or be completely automated.

The only explanation I can think of is that there is evolutionary pressure against using easy to produce compounds to regulate the processes that vitamin D regulates. If the receptors to which calcitriol binds were replaced by different receptors so that other molecules would bind to it and those other molecules would be manufactured without sunlight by certain cells in the organism itself, then perhaps this process would be very vulnerable to diseases in which the molecules are overproduced.

i'm not sure why it should be so easy (in evolutionary terms) to get shortages of vitamin D. it's fat soluble, and we do a pretty good job of storing it up. in fact, the fatter you are, the harder it is to get vitamin D levels back up to normal if you were low. the fat simply acts as a sink. this is great if you spend your summers in the sun, with a minimum of clothing, eating the seasonal abundance, getting fat and storing up vitamin D. then in leaner times of winter, you can survive off your stored fat and vitamin D.

as for why vitamin D, maybe it just started off as a signal of energy availability. this makes perfect sense if you're zooplankton, as the UV forms as soon as your cholesterol gets exposed to a bit of UV. and for us higher organisms, it still may function as a proxy for energy availability.

 

[Reality_Patrol]

Great question.

I agree that fat solubility must be part of the answer. Any vital nutrient that can be stored in fat improves survivability in cold environments, thus is "favored" by natural selection.

But I think there must be a deeper aspect to. I'm thinking something unique about molecular properties that can only be derived by a UV photo-initiated synthesis process.

Just some thoughts...RP

 

[Jeniffer]

I think vitamin D helps in fat-soluble prohormones. Other sources are D2 and D3 as well. Finding the best vitamin supplements is directly correlated to the purpose of intake.

 

[Blenton]

So?

Remember that humans have lived in a warm a and sunny climate for most of our history, so getting enough vitamin D was not a problem. This means there was no evolutionary pressure to "develop" an alternative mechanism.

What about the thousands of years of ice age?

 

[DaveC426913]

What about the thousands of years of ice age?

Ice age does not directly equate with lack of sunlight.

1] Take note that cold days are often actually associated with sunny days. Clouds keep heat in. Clear skies let heat out.

2] Ancient man did not have the luxury of ordering pizza and "cocooning" during cold spells. One could conceivably argue that ice ages might see a rise in sun exposure, since they'd have to spend more time hunting for scarce food.

 

[Count Iblis]

The question is really why e.g. immune cells have evolved in such a way as to be activated by vitamin D. If you have enough Vitamin D the part of your immune system that actively seeks out new threats and destroys them becomes more active.

Perhaps this is because of Proton Soup's energy argument. A more active immune system uses more energy. A shortage of vitamin D could be associated with the Winter season and the prosepect of food shortages. Under those conditions, you may want to build up or conserve fat reserves rather than using energy to let your immune system work overtime.

 

[Blenton]

Ice age does not directly equate with lack of sunlight.

True, but Ice Age doesn't mean go outside in shorts. They'd be generously rugged up.

 

[runner]

Here's the Earth at glacial maximum. It looks like there are other areas around the globe where man could have been relatively free of selection pressures from the ice.

http://en.wikipedia.org/wiki/File:IceAgeEarth.jpg